The present invention relates to a hill start assistance device for a vehicle.
It relates more specifically to a hill start assistance device for a motor vehicle with a manual gearbox, based on a hydraulic braking circuit.
In present-day vehicles, hill starts (or pulling away on a hill) are a source of stress for the user of the vehicle who is trying his best to limit how far his vehicle rolls back.
In general, he has to transfer his foot as quickly as possible from the brake pedal to the accelerator pedal so that the vehicle does not have time to roll down the slope.
Solutions for avoiding this source of stress are known.
Document DE 102 42 122 proposes a method in which brake release is performed as a function of the torque transmitted to the clutch. For that, the method initially determines the longitudinal force exerted on the wheels and the inertia force exerted on the vehicle when the latter is stationary, and then, having estimated the engine torque, deduces the instantaneous torque transmitted to the clutch. If the transmitted torque thus calculated is high enough to compensate for the longitudinal force due to the slope, then the device releases the brakes.
This method does, however, have the disadvantage of being sensitive to clutch wear and aging.
Document EP 1 410 940 for its part proposes a method in which the braking is electrically controlled in order to maintain a demanded pressure on the wheel calipers, without the operator having to operate the brake pedal, so as to prevent the vehicle from moving, this being done until such time as the clutch pedal crosses a set threshold.
Document DE 196 21 628 discloses a device in which, when the brake pedal is first of all actuated, with the vehicle immobilized, a braking force is maintained at at least one wheel of the vehicle independently of the actuating travel of the pedal. When the brake pedal is then released, the braking force is reduced at said at least one wheel, allowing for a smooth start. To implement this method, the electrically operated valves of the braking system are controlled directly by the device.
Finally, document WO 2004/103785 describes a hill start assistance method in which a pitch sensor is used to deactivate a function that holds the vehicle on a hill, of the type commonly known by its English name of “hill-holder”. The vehicle is held in position until such time as set pull-away conditions have been satisfied, and until such time as a pitch change threshold is crossed.
However, the measurement of the pitch angle is highly sensitive to noise, due, for example, to movements of the passengers inside the vehicle. Furthermore, the pitch angle sensor has a high response time, making optimal brake release during pull-away difficult.